1. Field of the Invention
The present invention relates to the tanning of fish skins.
2. Description of the Prior Art
Up to 1930's (and indeed later in wartime Germany) there was a substantial interest in the tanning of fish skins to try to provide an alternative to animal skins for a variety of purposes, including foot wear, clothing and accessories. However, none of the processes suggested or employed were particularly successful in producing high quality items and, with the exception of shark skins which are tanned commericially, for example in Japan, there has been little or no interest in tanning of fish skins since the end of World War II.
Early suggestions for tanning of fish skins include those of U.S. Pat. Nos. 1,256,794, 1,467,858 and 2,633,730. In the process of U.S. Pat. No. 1,467,858 skins were tanned after preliminary treatments with sodium sulfide, lime and hydrochloric acid followed by bating. In the process of U.S. Pat. No. 1,467,858 fish skins were chrome tanned after treatment with lime and then acid, and after tanning the skins were treated with thiosulfate or soda. In the process of U.S. Pat. No. 2,633,730 the skins were treated with a pancreatic enzyme and then tanned with a vegetable extract, a syntan or after pickling and bleaching with a chrome tan. It is suggested that a combination of tannages, for example formaldehyde and chrome combinations may be used. French Pat. No. 729,942 abstracted in Chemical Abstracts volume 27 at column 439.sup.8 described the tanning of fish skins with synthetic tanning agents and then with vegetable tanning agents or a mixture of the two followed by chrome tanning.
More recently one of the rare disclosures in this field has been U.S. Pat. No. 2,700,590 which teaches the use of high astringency tanning agents such as a combination of cutch extract, quebracho extract and a phenol sulfonic acid formaldehyde condensation product.
The skin structure of teleost fishes (which comprise most common species of bony fish except sturgeon) differs from that of mammals and sharks, and it is this difference which has hitherto prevented the production of satisfactory high quality tanned products from the skins of such fishes. A brief description of the peculiarities of such skins is given in U.S. Pat. No. 2,700,590. In particular, it should be noted that fish collagen is very sensitive to hydrolysis.